The effect of interferon induction in newborn piglets on the humoral immune response to oral vaccination with transmissible gastroenteritis virus.

Groups of newborn piglets were vaccinated orally with a modified live transmissible gastroenteritis (TGE) virus vaccine at 3 days and 13 days of age, and treated with the synthetic interferon (IFN) inducer polyinosinic:polycytidylic acid (poly ICLC) at 2, 3 or 4 days of age. Control groups consisted of piglets which were vaccinated but not treated with poly ICLC, as well as piglets which were treated with poly ICLC but not vaccinated. Significantly higher mean IFN titres were produced in response to induction at 3 or 4 days of age than at 2 days, and the mean IFN titre of the vaccinated piglets treated with poly ICLC at 3 days of age was significantly higher than in the unvaccinated piglets which were treated at the same time. The mean TGE virus neutralizing antibody titres in the vaccinated piglets which were treated with poly ICLC on the day before vaccination were significantly lower than the mean titres in the untreated vaccinated piglets 10 and 14 days after the first dose of vaccine. The mean titres in the vaccinated piglets which were treated with poly ICLC at 3 or 4 days of age did not differ significantly from those in the untreated vaccinated piglets. The piglets which were treated with poly ICLC on the day after vaccination developed severe diarrhoea which persisted for 5-7 days.